Motion Control of Hydraulic Winch Using Variable Displacement Motors

The paper II is excluded from the dissertation with respect to copyright.To compete in the open market of the offshore crane industry, it is imperative for the manufacturer to continuously improve crane operability. In this context, the crane operability is expressed by means of a so-called weather window. The weather window is computed from the crane characteristics in combination with that of the vessel and the payload to be handled. It returns a set of boundaries for when it is accepted to perform a planned lift, mainly in terms of current sea-state and wind. The most important crane operability characteristics that enter into the computation of the weather window are maximum wire velocity and load capacity. This thesis focuses on how to improve the operability of active heave compensated offshore cranes. Two ways of achieving that goal have been investigated, namely, an improved control strategy and the use of model-based lift planning. The system investigated is the hydraulic active/passive winch system used by National Oilwell Varco. A new control strategy for the system was developed, tested, and implemented. The new strategy utilizes that variable displacement of the hydraulic motors of the active system of the winch drive. The strategy, semi secondary control, gave significant benefits in terms of reduced peak-pressure, increased load capacity, increased wire-speed capacity, and smoother winch performance at low winch speed. The results were validated and verified through simulations and in-field measurements.publishedVersio

Interdisciplinary design methodology for systems of mechatronic systems focus on highly dynamic environmental applications

This paper discusses a series of research challenges in the design of systems of mechatronic systems. A focus is given to environmental mechatronic applications within the chain “Renewable energy production - Smart grids - Electric vehicles”. For the considered mechatronic systems, the main design targets are formulated, the relations to state and parameter estimation, disturbance observation and rejection as well as control algorithms are highlighted. Finally, the study introduces an interdisciplinary design approach based on the intersectoral transfer of knowledge and collaborative experimental activities

Performing heavy transfers for offshore wind maintenance

As offshore wind farms become larger and further from the shore, there are strong economic and climate incentives to perform transfers required for operations and maintenance from floating vessels, rather than employing expensive and slow jack up rigs. However, successful transfers of heavy and sensitive equipment from a floating vessel (in all but benign sea/wind conditions) are heavily dependent on multiple degrees of freedom, high performance control. This project aims to bring a novel modelling and simulation methodology in Simulink that could be used to assess offshore wind installation and maintenance procedures. More specifically, the goal is to demonstrate that a crane prototype assumed to be located on a floating ship can transfer loads of hundreds of tons onto a fixed platform. Furthermore, this process should be completed with good precision and minimal impact force during equipment loading onto the stand. This problem has not yet been answered in research, with the only relevant patent in the field being the Ampelmann platform, a motionless bridge allowing technicians to access the offshore turbine. The first main contribution to knowledge of this thesis was the design of a 90 m crane that could handle a 660 tons load. This thesis presents a procedure, based on both mechanical/hydraulics design as well as empirical findings, which could be re-used for scaling the crane model to a more realistic dimension. It is worth noting that the goal here was to assess whether a realistically weighing piece of equipment could be stably handled, while the actual size of the crane was deemed unimportant. Another missing gap in literature this project wanted to fill was achieving active motion compensation for a larger scale system such as the current one. This refers to balancing out the base motions on multiple axes, so the payload can be moved on a given trajectory unaffected by them. Currently, research in the field mainly consists of crane mechanisms that feature active heave compensation, which only refers to the vertical axis. Hence, two control design methods were employed to assess the viability of heavy payload positioning from floating vessels through the development of a simulation approach using Simulink. The crane prototype was designed and modelled to operate under simulated vessel motions given by sea states with a significant wave height of 5 m and maximum wave frequency of 1 rad/s. Then, traditional control (feedback and feedforward) was designed to achieve active motion compensation with steady-state position errors under 20 cm. A second controller architecture was then designed/implemented as a comparison basis for the first one, with the aim being to find the most robust solution of the two. The nonlinear generalised minimum variance (NGMV) control algorithm was chosen for control design in this application. Due to its ability to compensate for significant system nonlinearities and the ease of implementation, NGMV was a good candidate for the task at hand. Tuning controller parameters to stabilize the system could also be based on the previously determined traditional control solutions. An investigation of controllers’ robustness against model mismatch was carried out by introducing various levels of uncertainty which influence actuators’ natural frequency to assess system sensitivity. The outcome of the investigation determined that traditional and NGMV controllers provided comparable regulating performance in terms of reference tracking and disturbance rejection, for the nominal case. This confirmed the assertion that the PID-based NGMV weightings selection is a useful starting point for controller tuning. Increasing the mismatch between the nominal system based on which the controllers’ were designed and the actual plant showed that the traditional control was marginally more robust in this application. The final contribution to knowledge this thesis aimed to bring was minimising the impact force during load placement on a fixed and rigid platform. To that end, the contact forces between the payload and a platform were first successfully modelled and measured. A switching algorithm between position and force control was then developed based on a methodology found in literature but on a microscopic scale project. To execute smooth load placement, an automated hybrid force/position control scheme was implemented. The proposed algorithm enabled position control on x and y axes, while minimising impact forces on the z-axis. Unfortunately, preliminary findings showed that there is still work to be done to claim any success in this regard. However, the author hopes this offers a good starting point for future work.As offshore wind farms become larger and further from the shore, there are strong economic and climate incentives to perform transfers required for operations and maintenance from floating vessels, rather than employing expensive and slow jack up rigs. However, successful transfers of heavy and sensitive equipment from a floating vessel (in all but benign sea/wind conditions) are heavily dependent on multiple degrees of freedom, high performance control. This project aims to bring a novel modelling and simulation methodology in Simulink that could be used to assess offshore wind installation and maintenance procedures. More specifically, the goal is to demonstrate that a crane prototype assumed to be located on a floating ship can transfer loads of hundreds of tons onto a fixed platform. Furthermore, this process should be completed with good precision and minimal impact force during equipment loading onto the stand. This problem has not yet been answered in research, with the only relevant patent in the field being the Ampelmann platform, a motionless bridge allowing technicians to access the offshore turbine. The first main contribution to knowledge of this thesis was the design of a 90 m crane that could handle a 660 tons load. This thesis presents a procedure, based on both mechanical/hydraulics design as well as empirical findings, which could be re-used for scaling the crane model to a more realistic dimension. It is worth noting that the goal here was to assess whether a realistically weighing piece of equipment could be stably handled, while the actual size of the crane was deemed unimportant. Another missing gap in literature this project wanted to fill was achieving active motion compensation for a larger scale system such as the current one. This refers to balancing out the base motions on multiple axes, so the payload can be moved on a given trajectory unaffected by them. Currently, research in the field mainly consists of crane mechanisms that feature active heave compensation, which only refers to the vertical axis. Hence, two control design methods were employed to assess the viability of heavy payload positioning from floating vessels through the development of a simulation approach using Simulink. The crane prototype was designed and modelled to operate under simulated vessel motions given by sea states with a significant wave height of 5 m and maximum wave frequency of 1 rad/s. Then, traditional control (feedback and feedforward) was designed to achieve active motion compensation with steady-state position errors under 20 cm. A second controller architecture was then designed/implemented as a comparison basis for the first one, with the aim being to find the most robust solution of the two. The nonlinear generalised minimum variance (NGMV) control algorithm was chosen for control design in this application. Due to its ability to compensate for significant system nonlinearities and the ease of implementation, NGMV was a good candidate for the task at hand. Tuning controller parameters to stabilize the system could also be based on the previously determined traditional control solutions. An investigation of controllers’ robustness against model mismatch was carried out by introducing various levels of uncertainty which influence actuators’ natural frequency to assess system sensitivity. The outcome of the investigation determined that traditional and NGMV controllers provided comparable regulating performance in terms of reference tracking and disturbance rejection, for the nominal case. This confirmed the assertion that the PID-based NGMV weightings selection is a useful starting point for controller tuning. Increasing the mismatch between the nominal system based on which the controllers’ were designed and the actual plant showed that the traditional control was marginally more robust in this application. The final contribution to knowledge this thesis aimed to bring was minimising the impact force during load placement on a fixed and rigid platform. To that end, the contact forces between the payload and a platform were first successfully modelled and measured. A switching algorithm between position and force control was then developed based on a methodology found in literature but on a microscopic scale project. To execute smooth load placement, an automated hybrid force/position control scheme was implemented. The proposed algorithm enabled position control on x and y axes, while minimising impact forces on the z-axis. Unfortunately, preliminary findings showed that there is still work to be done to claim any success in this regard. However, the author hopes this offers a good starting point for future work

ALTERNATIVE AND FLEXIBLE CONTROL METHODS FOR ROBOTIC MANIPULATORS: On the challenge of developing a flexible control architecture that allows for controlling different manipulators

Robotic arms and cranes show some similarities in the way they operate and in the way they are designed. Both have a number of links serially attached to each other by means of joints that can be moved by some type of actuator. In both systems, the end-effector of the manipulator can be moved in space and be placed in any desired location within the system’s workspace and can carry a certain amount of load. However, traditional cranes are usually relatively big, stiff and heavy because they normally need to move heavy loads at low speeds, while industrial robots are ordinarily smaller, they usually move small masses and operate at relatively higher velocities. This is the reason why cranes are commonly actuated by hydraulic valves, while robotic arms are driven by servo motors, pneumatic or servo-pneumatic actuators. Most importantly, the fundamental difference between the two kinds of systems is that cranes are usually controlled by a human operator, joint by joint, using simple joysticks where each axis operates only one specific actuator, while robotic arms are commonly controlled by a central controller that controls and coordinates the actuators according to some specific algorithm. In other words, the controller of a crane is usually a human while the controller of a robotic arm is normally a computer program that is able to determine the joint values that provide a desired position or velocity for the end-effector. If we especially consider maritime cranes, compared with robotic arms, they rely on a much more complex model of the environment with which they interact. These kinds of cranes are in fact widely used to handle and transfer objects from large container ships to smaller lighters or to the quays of the harbours. Therefore, their control is always a challenging task, which involves many problems such as load sway, positioning accuracy, wave motion compensation and collision avoidance. Some of the similarities between robotic arms and cranes can also be extended to robotic hands. Indeed, from a kinematic point of view, a robotic hand consists of one or more kinematic chains fixed on a base. However, robotic hands usually present a higher number of degrees of freedom (DOFs) and consequentially a higher dexterity compared to robotic arms. Nevertheless, several commonalities can be found from a design and control point of views. Particularly, modular robotic hands are studied in this thesis from a design and control point of view. Emphasising these similarities, the general term of robotic manipulator is thereby used to refer to robotic arms, cranes and hands. In this work, efficient design methods for robotic manipulators are initially investigated. Successively, the possibility of developing a flexible control architecture that allows for controlling different manipulators by using a universal input device is outlined. The main challenge of doing this consists of finding a flexible way to map the normally fixed DOFs of the input controller to the variable DOFs of the specific manipulator to be controlled. This process has to be realised regardless of the differences in size, kinematic structure, body morphology, constraints and affordances. Different alternative control algorithms are investigated including effective approaches that do not assume a priori knowledge for the Inverse Kinematic (IK) models. These algorithms derive the kinematic properties from biologically-inspired approaches, machine learning procedures or optimisation methods. In this way, the system is able to automatically learn the kinematic properties of different manipulators. Finally, a methodology for performing experimental activities in the area of maritime cranes and robotic arm control is outlined. By combining the rapid-prototyping approach with the concept of interchangeable interfaces, a simulation and benchmarking framework for advanced control methods of maritime cranes and robotic arms is presented. From a control point of view, the advantages of releasing such a flexible control system rely on the possibility of controlling different manipulators by using the same framework and on the opportunity of testing different control approaches. Moreover, from a design point of view, rapidprototyping methods can be applied to fast develop new manipulators and to analyse different properties before making a physical prototype

Underwater Vehicles

For the latest twenty to thirty years, a significant number of AUVs has been created for the solving of wide spectrum of scientific and applied tasks of ocean development and research. For the short time period the AUVs have shown the efficiency at performance of complex search and inspection works and opened a number of new important applications. Initially the information about AUVs had mainly review-advertising character but now more attention is paid to practical achievements, problems and systems technologies. AUVs are losing their prototype status and have become a fully operational, reliable and effective tool and modern multi-purpose AUVs represent the new class of underwater robotic objects with inherent tasks and practical applications, particular features of technology, systems structure and functional properties

Simulation, testing and validation of digital displacement hydraulic power take-off for wave energy converters

Whilst the available global wave power resource is significant at over 2 TW, there has been very little exploitation of it to date for the generation of electricity. This is due in part to the challenge of converting energy from a low speed, high force, variable source to synchronous, grid-quality electricity. The power take-off (PTO) is the subsystem of the wave energy converter (WEC) which carries out this conversion from mechanical to electrical energy. There are many competing requirements for the design of PTOs, but amongst them are efficiency, load-handling capability, controllability and scalability. The very high ratio of peak-to-mean powers involved means that the system must be able to respond efficiently across a broad load range. Hydraulic systems are a good choice for PTO design as they have very high power densities and are naturally suited to high-force applications. The Quantor is a novel hydraulic WEC PTO concept which combines the quantised PTO of the ‘Pelamis’ WEC with Digital Displacement (DD) hydraulic pump-motors developed by Artemis Intelligent Power Ltd (AIP). The Quantor should be an efficient PTO that is fully controllable in all four quadrants and is offers power conversion improvements to a broad range of WEC designs. This project aims to demonstrate the technical feasibility and quantify the performance of the Quantor, using a WEC emulator to test it in representative conditions. First, modelling is carried out of the WEC emulator for design purposes, followed by detailed physical modelling of the envisaged Quantor PTO system. This means the design of the hydraulic circuit can be refined, the control system can be developed and initial efficiency estimates obtained. After verifying the Quantor in simulation, the WEC hardware-in-the-loop (HIL) emulator and laboratory-scale Quantor system are constructed and commissioned. The WEC emulator system is shown to be a successful test facility for the Quantor PTO. Extensive testing is carried out in both regular and irregular wave conditions and a range of control modes to quantify the performance of the Quantor PTO. The measured input shaft to generator shaft efficiency exceeds 70% in many cases above a minimum absorbed power threshold. Using the data from testing, efficiency results and a detailed loss breakdown for the Quantor in different operating conditions are produced. The physical model is then validated from this data, in terms of its efficiency and losses. The validated physical model replicates the applied PTO torque and overall efficiency of the Quantor within 5% of the experimental results across the tested power range (approximately 2 to 40 kW of input mechanical power). After this, a simplified model is produced which replicates the tested PTO torque, efficiency and losses, but can be used to estimate the Quantor performance in various full-scale WEC architectures. This means that reliable PTO performance predictions based on experimental data can be produced for systems other than the laboratory-scale Quantor. The existence of this Quantor PTO with; the ability to efficiently operate in all four quadrants as demanded by a controller; the availability of a detailed loss breakdown; and the capability to model future system architectures, may provide future opportunities for wave energy developers to design and install commercially successful WECs

Estimation and Verification of Hydrodynamic Parameters of an ROV using CFD

The hydrodynamic added mass and damping of a Remotely Operated Vehicle (ROV) are estimated using Computational Fluid Dynamics (CFD) based on OpenFOAM. The estimated hydrodynamic parameters are verified with recorded data from an operating ROV at Snorre B (SNB). Then, the added mass and damping are adjusted to assess if a more accurate fit with the recorded data can be obtained. The ROV under investigation is the Merlin UCV, a work-class ROV. The UCV is first simplified to perform CFD. Two simplified versions are made, and the thin side plates are included in the more complex version. Two mesh convergence studies are conducted to verify the mesh and the computational domain. The Reynolds number is set to be $2.25 \times 10^6$. Numerical simulation based on Steady- and Unsteady-Reynolds-Averaged Navier–Stokes combined with the k-$\omega$ Shear Stress Transport (SST) turbulence model are performed to obtain the hydrodynamic parameters. By studying the influence of the side plates, it is found that the drag increases considerably when the plates are directly exposed to the flow. When there is a constant flow in sway, the value of $C_d$ is 1.4682 when the side plates are not considered. However, when side plates are introduced, the value of $C_d$ increases by 15 \% to 1.6880. Three different experiments are recreated numerically to find the added mass and damping in all Degrees Of Freedom (DOF) as a result of respective acceleration and constant velocity in the corresponding direction. The first numerical simulation is the towing tank test conducted to find the damping in the translational directions. Steady-Reynolds-Averaged Navier–Stokes (RANS) is used, and a constant velocity in the applicable directions are implemented. Then, rotating arm simulations are conducted to find the damping in the rotational directions. A similar procedure is used for the towing tank simulations, but a constant angular velocity is implemented. Planar Motion Mechanism (PMM) simulations are performed to obtain the added mass and inertia in all 6 DOF. Oscillatory linear and angular movements are executed to find the added mass and inertia in the translational and rotational directions. Since the movement is oscillatory, Unsteady-Reynolds-Averaged Navier–Stokes (URANS) is used to capture the time-varying flow. Furthermore, the numerical model used to estimate hydrodynamic parameters is validated by being compared to recorded data of an operational ROV at SNB. The recorded data were logged using the SPRINT, consisting of linear and angular position and velocity. A simulator code built on the classical equations of motion is made to simulate the movement data. Moreover, the CFD estimated added mass and damping are implemented in the equations. In the present study, the simulated movement of the ROV is later fitted with the recorded data. The fit between the recorded and simulated movement is satisfactory using the CFD estimated parameters. The added mass and damping are then adjusted, and an improved fit with the recorded data is achievable. Therefore, the conclusion is to adjust the hydrodynamic parameters if recorded data is available. This method is more efficient than CFD and gives more accurate results. However, if recorded data is unavailable, CFD can provide an efficient method to accurately predict the damping and added mass.Masteroppgave i havteknologiHTEK3995MAMN-HTEKMAMN-HTE

ESSE 2017. Proceedings of the International Conference on Environmental Science and Sustainable Energy

Environmental science is an interdisciplinary academic field that integrates physical-, biological-, and information sciences to study and solve environmental problems. ESSE - The International Conference on Environmental Science and Sustainable Energy provides a platform for experts, professionals, and researchers to share updated information and stimulate the communication with each other. In 2017 it was held in Suzhou, China June 23-25, 2017

Floating offshore wind farm installation, challenges and opportunities : a comprehensive survey

The deployment of floating offshore wind farms marks a pivotal step in unlocking the vast potential of offshore wind energy and propelling the world towards sustainable energy solutions. Despite the compelling prospects of floating wind technology, its implementation is challenging. Complex installation procedures, associated high costs, and evolving regulations can hinder widespread adoption. However, these challenges present opportunities for innovation and cost reduction. This paper delves into the technical, operational, and economic aspects of floating offshore wind farm installation, providing a comprehensive overview of the current state-of-the-art. The analysis goes beyond simply describing the current landscape by critically examining the complexities involved in floating offshore wind farm installation. It identifies critical research areas for advancing floating wind technology towards broader adoption and greater efficiency. The findings underscore the critical need for standardised foundation designs, advanced installation methods, and robust collaboration between academia and industry. By fostering such collaboration, for example, by creating research consortiums or knowledge-sharing platforms, the floating wind industry can accelerate advancements and unlock its full potential as a clean and sustainable energy source